Direct current triode voltage regulator



Jan. 2, 1968 c. o. JORGENSEN 3,

DIRECT CURRENT TRIODE VOLTAGE REGULATOR Filed Aug. 30, 1965 l3 10 LOAD ILOAD n aoovoc '4 SOURCE CLINTON o. JORGENSEN INVENTOR.

AGENT United States Patent Calif., assignor to Bristol, Pa, a corpora-ABSTRACT OF THE DISCLOSURE A direct current, common cathode triodevoltage regulator connected across the load in which the conduction ofthe triode is responsive to an adjustable negative biasing source andalso to feedback from the anode of the triode through a parallel RCcircuit.

This invention relates to improved voltage regulators and moreparticularly to improved triode voltage regulators for use with directcurrent power supplies.

In much of the contemporary electronic equipment, it is generallyrecognized that changes or fluctuations in operating voltages frequentlyhave an adverse effect on the performance characteristics of suchequipment. For example, in electronic switching devices such asmultivibrators it is common practice to supply both the load andvoltage-sensitive timing circuits from the same power source. Switchingaction produces abrupt and at times wide ranging load changes whichcauses substantial supply voltage fluctuations and correspondingvariations in switc ing periodicity. Thus, when precision switchingperiods are desired, it becomes necessary to regulate operating voltagelevels to within narrow limits usually determined by the degree ofprecision required.

' Apparatus for regulating DC supply voltages appear in several forms.One well known means includes vacuum tube type voltage regulators.Output voltage regulation by this means is frequently accomplished byemploying gasfilled VR (voltage regulator) tubes in combination withother elements in the regulating circuits. Generally, the VR tubes havea standard operating threshold fixed at such values as 75, 90, 108 or150 volts DC, thereby limiting the choice of operating voltage levelsand causing the user to frequently compromise on the selection of loaddesign parameters. Moreover, these tubes in themselves are known to beincapable of regulating a 300 volt DC power supply any closer than about1.5 to 3% of the supply voltage. Closer regulation may be had bycascading the VR tubes or employing zener diodes in the regulatingcircuits. This is done at the expense of increased complexity,unreliability and cost of manufacturing such devices, in addition, toretaining the aforementioned limitations on choice of operating voltagelevels.

It is, therefore, an object of this invention to provide for an improvedvoltage regulator having a lower equivalent source impedance for usewith a direct current power supply.

Another object of this invention is to provide an improved triodevoltage regulator having a selectable operating voltage level yetcapable of maintaining its output voltage Within narrower limits thancomparable prior art devices.

Another object of this invention is to provide a simple, versatile,reliable and inexpensive triode voltage regulator having good regulatingcharacteristics.

Still another object of this invention is to provide an improved triodevoltage regulator having a grounded cathode thereby eliminating a biasedheater supply and improving safety of operation with respect topotential differences between cathode and heater.

These and other objects and advantages will become apparent from thefollowing description taken in connection with the accompanying singlefigure drawing which shows an embodiment of the invention.

Briefly, this invention contemplates achieving the foregoing objects byemploying a triode amplifier tube as a voltage regulator in shunt withthe load in a circuit where triode conduction is established initiallyfrom an adjustable biasing source and varied responsive to outputvoltage changes by the control grid in opposition to changes in loadcurrent. This action maintains essentially a constant current flowingfrom a DC power source through a voltage dropping resistor to both avariable load and the anode of said triode. The regulated output voltageis taken across the anode and cathode, the latter being grounded forsafety of operations.

Referring to the drawing, there is shown a schematic diagram of a triodevoltage regulator circuit for achieving the foregoing objects. Twintriode 10, a medium mu Class A1 amplifier tube such as an RCA 5687, isemployed as voltage regulator for a 300 volt DC source 11. A triodehaving a singular electrode structure, or alternately one having high mucharacteristics, may also be used. Where the particular triode chosenhas dual electrode structures as in the circuit illustrated, theirrespective anodes, control grids and electron-emitting cathodes areconnected for parallel operation. For this reason, these elements willbe referred to below in the singular.

The anode of triode 10 is connected through voltage dropping resistor 12to the positive side of 300 volt DC source 11 at input terminal 19. Theelectron-emitting cathode is connected to a grounded conductor whichjoins negative source input terminal 20 to output terminal 17. Theheater, not shown, is connected to an unidentified voltage source. Thecontrol grid of triode 10 is connected to the juncture of resistors 13and 14 which form a voltage divider in a grid biasing and controlnetwork. The opposite end of resistor 14 is connected to biasing sourcewhich for convenience has been designated a minus volts DC, althoughvoltages as low as minus 50 volts DC may be employed. Resistor 13 isshunted by compensating capacitor 15 and its remaining end is connectedto the anode of triode 10. Terminals 16 and 17 are respectivelyconnected to the anode and ground across which the regulated outputappears. Load 1 is connected across output terminals 16 and 17 throughseries load resistor 18. Additional loads identified as Load itconnected through series load resistor Rn may also be connected acrossthe output terminals up to the capacity of source 11.

A mode of operation will be described after first assuming, for example,that triode 10 is in fact an RCA 5687; the nominal regulated outputvoltage at terminal 16 is +200 v. DC; that Load 1 and Load 12 aremultivibrators varying between 10 and 20 ma. and 2 and 20 ma.,respectively, at random, coincident intervals. Other circuit componentsare: capacitor 1550 pf and the resistance values of resistors 12-21200ohms, 13-220,000 ohms, l i-140,000 ohms, Iii-8,200 ohms, and RN8,200ohms, respectively. It will be understood that these values are forillustrative purposes and are not to be construed as limiting in anysense.

In operation, the grid of triode 10 is responsive to both an adjustablebiasing voltage for pre-selecting a nominal anode voltage level and tochanges in anode voltage for maintaining this voltage level withinnarrow limits. Initially, let it be assumed that Load 1 is operating inits stable state and resistor 14 in the grid biasing and control networkis adjusted to produce about 14 volts bias on the grid. This establishesnominal triode conduction and permits a charge on capacitor 15 toaccumulate to a particular value. Triode conduction causes a nominalcurrent to flow through resistor 12 which hereinafter will be referredto as regulator current. Both regulator current and eXternal loadcurrent pass through resistor 12 and their sum normally remainsessentially constant and reduces source 11 voltage from +300 v. DC to anominal +200 v. DC at the anode of triode 10. Under steady supply andload current conditions, this maintains both grid and anod voltages atsteady values and maintains the output voltage across terminals 16 and17 within narrow limits.

A reduction in triode conduction takes place when grid bias is loweredto a greater negative value by adjusting resistor 14, or upon receivinga downward fluctuation in source 11 voltage level which lowers grid biasreference. Consequently, either condition decreases the current flowthrough resistor 12. Adjustment of resistor 14 has the effect of raisingthe nominal anode voltage to a value higher than the +200 volt level.The reduction in current flow through resistor 12 reduces the voltagedrop thereacross and substantially offsets the downward fluctuation insource 11 voltage level, thereby maintaining anode and output voltagesat the nominal level. The opposite action takes place when triodeconduction is increased by opposite adjustment of resistor 14 or anupward fluctuation in source 11 voltage level.

When load current increases, for example, by the sudden switching ofLoad 1 from its stable to its unstable state, the load current flowingthrough resistor 12 begins to increase. This is accompanied by a slightincrease in voltage drop across resistor 12 which has a tendency tolower the anode voltage below the +200 volt level while lowering gridbias at the junction between resistors 13 and 14 below -14 volts. Triode conduction decreases as does the regulator current flowing throughresistor 12, thus initiating a regulatory action which tends to maintainessentially the original current flow in, and voltage drop across,resistor 12. Because of the anode feedback connection to the grid andthe transconductance characteristics of triode 10, the regulatory actionstabilizes when anode voltage reaches about +1995 volts and grid voltageat about 14.2 volts. The degree of regulation may be improved byemploying a higher mu triode if the range of current variation issmaller. Thus, it will be observed that grid voltage varies directlyproportional to anode voltage and in effect inversely proportional toload current to maintain the output voltage at terminal 16 within anarrow limit of the nominal +200 volt level.

It should be noted that when load current suddenly increases, amomentary dip in output voltage would slowly occur because of reducedtriode conduction which is accompanied by a change in grid-to-cathodecapacitance charge. However, this dip is essentially prevented by theaction of compensating capacitor 15 which supplies current to instantlyreadjust the grid-to-cathode capacitance charge to a new level.

Further increases in load current, as for example by the initiation ofLoad n concident with Load 1, produces a corresponding increase incurrent flowing through resistor 12. As previously mentioned, this willcause a decrease in grid voltage which in this instance is driven tobelow 14.5 volts. Again this decreases both triode 10 conduction and theregulator portion of current flowing through resistor 12 and restoresanode voltage to about a volt less than the nominal +200 volt level.Theoretically, the output voltage can be maintained at about the +200volt level while load current increases until triode 10 ceases toconduct current. Thereafter, the total current flowing through resistor12 increases instead of remaining essentially constant and causes theanode voltage to decrease proportionally thereto.

Operation during a reduction in load current takes place under oppositeconditions from the foregoing. For example, as Load 11 is removed fromoutput terminals 16 and 17, anode voltage rises from a level of about+199 volts a d grid voltage rises from below 14.5 volts, the

latter causing triode 10 to conduct more heavily and increase theregulator current portion of current flowing through resistor 12. Thisincrease in regulator current substantially oifsets the reduction inload current flowing through resistor 12 and raises the anode voltagetoward the nominal +200 volt level. As load current drops 011 thisaction continues until the original nominal output voltage level isattained.

Under the foregoing conditions, this simple voltage regulator circuitprovides a regulation of between /s% and /2 of the supply voltage acrossoutput terminals 16 and 17 when using an RCA 5687 as triode 10. Closerregulation is of course obtainable by using a higher mu triode havingadequate maximum power and current ratings. This is because of thegreater sensitivity provided by the higher ratio of anode currentchanges to grid voltage changes. Further, while reference has been madeto a nominal output voltage of 200 volts DC, other voltage levels may behad within the limits of triode 10 by adjusting the value of resistor 14to a new value as desired.

Moreover, it should be noted that because triode 10 is acting as a shuntregulator rather than a series regulator and the fact that its cathodeis grounded, operational safety and reliability are improved withrespect to voltage differences that otherwise would exist betweencathode and heater. Many tubes are limited to volts or less cathode toheater rating. Therefore, a separately biased heater voltage sourcewould be required for higher voltages. This detracts from the ease ofutilizing a simple voltage regulator with a varying source and load andfurther emphasizes the advantages offered by this invention.

Although the present invention has been described with a certain degreeof particularity, it is understood that changes may be made in circuitdetails without departing from the spirit and scope of the invention ashereinafter claimed.

What is claimed is:

1. A voltage regulator for a direct current supply system having a DCsource connected in a circuit to a load, said voltage regulatorcomprising:

a voltage dropping resistor connected in series between said source andsaid load;

a triode vacuum tube having medium to high mu characteristics and ananode, grid and an electron emitting cathode, said anode and saidcathode being connected across said load;

biasing means including an adjustable source of a negative voltageconnected to said grid for causing substantial tube conduction andcorresponding anode current flow through said voltage dropping resistort establish a nominal output voltage level as desired during the absenceof said load; and

means for supplying a control voltage to said grid, said means includinga resistor and a capacitor connected in parallel between said grid and apoint between said anode and said voltage dropping resistor forautomatically maintaining a substantially constant voltage drop acrosssaid voltage dropping resistor.

References Cited UNITED STATES PATENTS OTHER REFERENCES RCA ReceivingTube Manual, High Voltage Regulator Circuit, 1961, p. 51 relied on.

JOHN F. COUCH, Primary Examiner.

A. D. PELLINEN, Assistant Examiner.

